We propose to build and test a dynamic vascular optical tomographic imaging (DVOTI) system that can be used to detect and monitor peripheral arterial disease (PAD). PAD is estimated to affect approximately 8 to 12 million individuals in the United States. However, the disease is considerably under-diagnosed, since most patients are asymptomatic and no single reliable screening modality has been established. Most of the undiagnosed and untreated patients are diabetics. They commonly suffer from peripheral neuropathy and hence do not sense and report symptoms (such as pain) that are early signs of the disease. Consequently more than 60% (~65,000 per year) of all lower extremity amputations in the United States are performed in diabetic patients with PAD. With the number of diabetic patients expected to triple and reach almost 100 million by 2050, the problems related to undiagnosed PAD will only rise in the years to come The most widely used diagnostic test for PAD, determination of the ankle-brachial index (ABI) in conjunction with pulse-volume recordings (PVR), is known to be unreliable for diabetics. And even in non- diabetics, ABI with PVR and all other existing diagnostic tests (such as Duplex Ultrasound or Magnetic resonance angiography), only provides accurate information about proximal occlusions in major arteries of the leg. However, none of these tests assess the distal perfusion of the foot where most complications, such as ulcers and gangrene, typically occur. Monitoring the success of surgical interventions, such as angioplasty or bypass surgery, suffers from the same shortcomings, as physicians are limited to the same suite of tests that are inadequate to assess the perfusion of the foot. Dynamic VOTI promises to overcome the limitations of current diagnostic and monitoring techniques and has the potential to initiate a paradigm shift concerning how vascular diseases are assessed. In preliminary studies we have shown that DVOTI can provide three-dimensional time-series images that provide valuable information about the perfusion of the vascular bed in feet of PAD patients. The near-infrared light used in the instrument has no adverse health effects and measurements can be repeated frequently to monitor post interventional progress. Therefore, we believe that DVOTI will prove to be a safe and accurate method to diagnose and monitor PAD in non-diabetic and diabetic patients.